Method of forming a metallic surface on ceramic bodies



N0'vl.`25,z1941. n- H, ROWLAND 2,264,152

METHOD 0F FORMING A METALLIC SURFACE 0N CERAMIC BODIES Filed April 27,1958 Figi.

ME TAL [Z50 S URFACE Inventor Davicige vH Rowland,

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Patented-Nov. 25, 1941 METHOD 0F FORMING A METALLIC SUR- FACE 0N CERAMICBODIES l paviage n. Rowland, Baltimore, Md., assigner,

by mesne assignments, poration, Baltimore, Md.,

Maryland to Locke Insulator Oora. corporation of Application April 27,1938, Serial No. 204,618

(l. ill-70.2)

4 Claims.

It is desirable often to metalize the surface of a ceramic material,such as porcelain, for example, i. e.. to provide on a bodyor base ofsuch material a surface covering or coating of, metal. For example, thisis desirable frequently in connection with ceramic insulators forvarious reasons, such as the distribution of electric stress,elimination of corona, providing for grounding shields on bushings, andthe providing of places to which metal parts may be attached coatingand'metal is of the order of only a few thousandths of an inch, forVexample, .020".

. According to my invention, I provide on the portion of the porcelainsurface to which metal by soldering or brazing. Usually, it is desirableto apply metal to only a portion of the surface of the ceramic ware.

In metalizing ceramic surfaces, such as porcev lain surfaces, it isimportant that the metal adhere firmly to the ceramic body 4which meanstheremust be a good bond between the metal and the body. Otherwise, themetal may peel off, it being prone to do so becausel of the differencein coeillcients of expansion between metals and ceramic materials, suchas porcelain.

The object of the present invention is toprovide. an improved metalizedceramic surface wherein the metal is attached to the ceramic body with abond of great strength; to provide an improved method for applyingmetalv to ceramic bodies to form a metal covering thereon; and toprovide an improved ceramic coating for a ceramic body to which coatingthe metal For a considerationof what I believe' toI be novel andmyinvention, attention is directed to the following specification andthe claims appended thereto.

The invention is well adapted for use with porcelain insulators and itis this application of myv invention which I have elected tospecifically illustrate andrdescribe. It is to Vbe understood, however,that this is only by way of example and that the invention may becarried out in connection with porcelain ware or bodies of any desiredtype, and in connection with ware or bodies formed from ceramicsother-.than porce- In the drawing, Fig. i is a side elevation of aninsulator, the upper portion of which is provided with a metallizedsurface in accordance with my invention, and Fig. 2 is a. detailsectional view on a'much enlarged scale through a portion of themetalized porcelain surface.

Referring to the drawing, I indicates a porcelain insulator, 2 indicatesa ceramic coating on the insulator, and 3 indicates metal applied to theceramic coating. The metal may be copper.

aluminum or other metal, as desired. Most frequently, the metal used iscopper. In Fig. 2, the thicknesses off Ythe ceramic coating and metalare many times magnified for purposes of illustration. Actually, thethickness of the ceramic is to be applied a ceramic coating of acharacter such that it provides an outer surface having smallcrater-like indentations therein, which indentations are' to a veryconsiderable extent irregular in shape and undercut. The metal on thesurface of the porcelain fills these craterlike iindentations and isthus firmly bonded to the porcelain. This is illustrated on a muchenlarged scale in Fig. 2 wherein indicates indentations or craters inthe surface of the ceramic coating which are irregular in shape and to avery considerable extent undercut, and which are lled with the metal 3.

To provide the portion of the porcelain surface to be metalized with aceramic coating of the character described, 'I apply to the ware or bodybefore ring a ceramic mixture having a composition which is highlyrefractory. This I obtain by using a ceramic mixture or compositionhaving an excess of A1203 which may be supplied in the form of animpalpable calcined aluminum hydrate. By an excess of A lzOa, I meanthat the alumina content is so great compared to the .feldspar that atthe kiln temperature used for firing the insulator" or other device.there is not sufficient feldspar to dissolve it and therefore as theceramic coating hardens, there are lumps of undissolved aluminadistributed throughout the coating. As a result, theceramic mixture doesnot form a smooth glossy surface in the kiln but on the contraryprovides a vsurface with a dull ilnish and one which feels to the touchlike the finest grade of emery paper.

Under the microscope, nach a surface appears to have small crater-'likeindentaticns.' many o! which are undercut.

As a ceramic coating, I have found the following composition or formulasatisfactory:`

Percentage dry weight- Ball clay 10 Calcined aluminum hydrate 37Feldspar 37 F2201 2 Iron chromai'e 8.

To this mixture isadded 4% by dry weight of gum arabic and 1/2% by dryweight of `benzoio acid. The composition thus formed is mixed with watersumcient to form a-iuid of a density of 1.3. It is tobe understood thatthis formula is given only by way of example. Also, it is tov beunderstood that refractory materials other plied to the ware by beingbrushed or sprayed thereon, the latter method being preferable. vTheapplication should be just thick enough so that the porcelain will notshow through the coating when the ware is fired. The ware is fired atthe. kiln temperature and for the period in ordinary use for firingware.

When a porcelain body having a ceramic coating of the characterdescribed applied thereto is fired, it comes from the kiln with a dullfinish and rough surface as described above. I believe this to be due tothe ceramic coating melting and perhaps boiling while being fired in thekiln but which, because of its high viscosity, remains in its vesicularstate. I term a ceramic coating of this type a bubble coating. becauseit appears under a microscope that during the ming operation bubblesform in the glaze which at the surface burst out to leave minuteirregular cavities or craters in the surface of the coating.

After` the porcelain with the bubble coating thereon is removed from thekiln and cooled, the.

copper or other metal coating may be applied thereto by being sprayedthereon by any suitable process, such as the known Schcop' process. Whenthe copper is appiied..to the surface of the bubble coating, theminuteru'ndercut craters are filled with molten metal to which the mainmass of metal will adhere tightly, resulting in an excellent bondbetween the metal and the porcelain surface.

-I have found that a metalized surface formed vin accordance with myinvention is substantially superior to metalized surfaces formed byapplying metal to glazed surfaces which have been roughened by sandblasting or by embedding sand in the glaze. I believe this is to be dueto the fact that in my improved construction undercut craters are formedin the `surface which serve to firmly hold the metal. In addition, myimproved construction has the advantage that it.

may be provided at relatively low cost as compared to sand blasting orembedding sand in a g aze.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. The method of forming a'metalized surface on ceramic bodies whichcomprises applying to the ceramic body before it is fired a ceramiccoating composition including therein as one of the refractory materialsbetween 45% and 55% by weight of calcined aluminum hydrate reduced to animpalpablepowder, ring the ceramic body and coating at a temperaturesufficient to completely vitrify the said body, said temperature beingsuch that the said impalpable refractory materialis not entirelydissolved whereby there is provided a ceramic body having a. coating thesurface of which has minute undercut craterlike indentations, andapplying metal in molten form to the surface of such coating.

2. I'he method of forming a metalized surface on ceramic bodies whichcomprises applying to the ceramic body prior to firing the same acoating composition in which there is incorporated not less than 37% ormore than`55% by weight of pulverized aluminum oxide, firing the coatedceramic body to vitrify the said body whereby there is formed vin thesurface of said coating a plurality of undercut indentations, andsubsequently applying to said surface in spray form a metallic coating.

3. The methodof forming a metallic surface on ceramic bodies whichcomprises applying to an unred ceramic bodya, ceramic glaze coatingincluding therein pulverized calcined aluminum hydrate in an amountapproximately 45% by weight firing said coated body to completelyvitrify the same to thereby cause the said glaze composition to form ahighly refractory coating having a dull rough finish surface in whichare formed undercut crater-like indentatio'ns, and subsequently applyingthereto metal lin the form of a spray.

4. The method of forming a metaliicsurface on ceramic bodies whichcomprises applying -to an unred ceramic body a ceramic glaze coating.said coating including pulverized calcined aluminum hydrate and a flux,the calcined aluminum hydrate comprising approximately from 45% to byweight of said glaze coating whereby when said glaze coating is appliedto 'a ceramic body and the said coated body is fired so as to vitrifythe same there is provided a coating having in the surface thereof aplurality of undercut indentations, and subsequently applyingv theretometal in the form of a spray.

' DAV'IDGE H. ROWLAND.

